This invention concerns filters and more particularly liquid filters of a type including a filter media disposed in a tank into which liquid to be filtered is collected. The filter media often takes the form of a strip of paper or woven fabric material.
The filter media is disposed over a support having perforations or other openings allowing liquid to flow through the support after passing through the filter media to be filtered. The filtered liquid is collected in a space below the support.
A typical use is in filtering machining coolant/lubricant to remove chips and fine particles.
The chips or other solid debris accumulate atop the filter media and must be periodically removed from the tank.
In conventional filter apparatus of this type, a filter media belt is arranged to be periodically advanced incrementally to bring a section of the filter media to a location at one end of the tank where the chips and accumulated solids are discharged.
The filter media has taken two different forms, i.e. a woven fabric belt formed into an endless loop providing a “permanent” media and a disposable media comprised of a paper strip which fed in at one end of the tank and discharged for disposal at the other end.
The permanent media passes around a roller at each end of the tank so as to be recirculated through the tank with repeated indexing.
Periodic indexing of the filter belt allows the solids such as chips filtered out of the liquid to be progressively carried out of the tank by a series of incremental movements, and successive sections of the belt moved back into position for continued filtering.
The filter media also typically becomes clogged with fine solids after continued operation requiring cleaning of each section, as by being washed with clean liquid.
Disposable media is simply collected and discarded with the chips and other solids. This type of filter using a disposable media is described in U.S. Pat. No. 4,481,108 granted to the present inventor.
Disposable media filters may be more expensive to operate and entail a greater maintenance burden due to the need to stock and replace rolls of media and to collect and dispose of the used media.
For this reason, a filter apparatus using only permanent media belt filter may be lower in cost to operate and therefore may be preferable to some users, at least for some applications.
Filter apparatus using this type of filter media is shown in U.S. Pat. Nos. 6,066,255 and 4,390,428.
In some filter apparatus, both disposable and permanent media are used.
Both types of filter apparatus are sometimes provided with sealing to prevent dirty liquid from passing around the side edges of the filter belt or strip to allow dirty liquid to bypass the filtering action.
One type of seal comprises lengths of inflatable tubing extending along and over the side edge of the media which is inflated to press the media edges against a guide surface to seal the same, as described in the '108 patent referenced above. An inflatable filter belt seal is also shown in U.S. Pat. Nos. 4,390,428 and 5,601,729.
This type of edge sealing is effective but the tubing needs to be deflated during indexing to allow movement of the filter belt when a fresh belt segment is moved over the perforate support. This necessitates the use of control valves and a source of air pressure adding to the complexity and cost of the apparatus.
Depending on the size of the filter and the type of solids being filtered out, a conveyor may be required in addition to the filter media as in order to move a large volume of chips out of the tank. Typically, the conveyor comprises a series of vertical flight plates connected together with chain loops at either of the ends of the flight bars. The flight plates are arranged on edge and extending across the filter media and in engagement therewith to hold down and drive the bars media. The flights are primarily intended to act as a conveyor to carry large volumes of chips out of the tank.
The flights being made of metal are heavy, and their weight is used to hold the permanent media belt against the perforated support plate, as there may be a tendency for the belt to float up and allow dirty liquid to flow around the edges of the belt.
The flight conveyor chains and plates add substantially to the cost of the apparatus, as they must also be mounted, driven and controlled in similar fashion to the permanent media belt.
In other filter apparatus, such as shown in U.S. Pat. No. 6,066,255, drive chains are attached to the filter media belt to directly drive the same. This arrangement also is complicated and costly and sometimes causes bunching and wadding of the media belt, etc. as the belt may stretch or shrink relative the chain loops.
It is the object of the present invention to provide a low cost and simple filter apparatus of the permanent media belt type described.
It is another object to provide a filter media belt which simplifies the indexing drive and eliminates the need for a separate chip conveyor.